Botanical name: 

The leaves and tops of Hedeoma pulegioides (Linné,) Persoon (Nat. Ord. Labiatae). Common in American woods and waste places. Dose, 5 to 60 grains.
Common Names: Pennyroyal, American Pennyroyal, Squawmint, Tickweed.

Principal Constituent.—A fragrant volatile oil (Oleum Hedeomae).
Preparations.—1. Specific Medicine Pennyroyal. Dose, 5 to 60 drops.
2. Oleum Hedeomae, Oil of Pennyroyal. Dose, 2 to 10 drops.
3. Infusum Hedeomae, Infusion of Pennyroyal (1 ounce to Water, 16 fluidounces), ad libitum.
Specific Indications.—Amenorrhea of long standing, with pallor and anemia and dark circles around the eyes; the patient complains of languor, lassitude, takes cold easily, has pain in back and limbs, and exhibits full, prominent veins (Hennell); suppressed lochia.

Action.—Oil of pennyroyal produces toxic effects when given in overdoses. A drachm caused severe headache, difficult swallowing, intense nausea, severe retching without emesis, intolerable bearing down, laborlike pains, abdominal tenderness, constipation, dyspnea, semiparalysis of the limbs, and nervous weakness and prostration.

Therapy.—External. Oil of Pennyroyal is rubefacient and relieves the itching of insect bites. It is useful in embrocations for rheumatic pain. It is sometimes applied to the hands and face to protect against mosquitoes, fleas, and other insects. A cloth saturated with oil of pennyroyal may be hung in sleeping apartments to repel such insects.

Internal. Oil of Pennyroyal is useful in nausea, stomach cramps, flatulent colic, and amenorrhea in debilitated subjects. It is frequently used to prevent griping from other medicines. It may be given upon sugar or in emulsion. It and the dilution in alcohol are also credited with calmative properties in spasmodic cough, whooping cough, and in hysteria from menstrual debility. A drachm of the specific medicine given in hot water is the most certain agent we possess to restore suppressed lochia. The infusion is a popular and pleasant remedy for acute colds. It acts chiefly as a diaphoretic, and for this effect it is one of the most certain of medicines; and a relic of domestic methods once in favor among physicians, as well as the laity.

The Eclectic Materia Medica, Pharmacology and Therapeutics, 1922, was written by Harvey Wickes Felter, M.D.